Members of the fractured London 2017 board warned of “significant risk” to the delivery of next year’s World Athletics Championships and an “embedded near-irreconcilable conflict of interest” at the heart of the organisation in their resignation letter, the Guardian can reveal.

As the London 2017 managing director, Sally Bolton, became the latest executive to quit, just 18 months before the championships, a leaked resignation letter to the acting sports minister, David Evennett, by the deputy chair Heather Hancock and independent director Martin Stewart last week has laid bare the depth of the hostility on the board.

Amid a power struggle between the UK Athletics chairman, Ed Warner, and the chief executive, Niels de Vos, on one side and Hancock and Stewart on the other over a range of financial, sponsorship and governance issues, the depleted board will meet on Friday to plot a way forward.

The Guardian revealed last month that concern over the dual roles of Warner and De Vos was behind the decision by the International Association of Athletics Federations, mired in its own crisis, to refuse a request for funding help until the governance issues are resolved.

In the letter, Hancock reveals that she was given clear instructions by the former sports minister Hugh Robertson “to ensure the delivery of the championships was not sublimated to UKA’s interests”.

But they say that the “inherent conflict of interest” in the multiple roles assigned to UKA had created “significant delivery risk” and compromised “transparency, scrutiny and accountability”.

The letter goes on to say they had been forced to refuse a request to pay UKA for commercial services they were no longer going to provide and to intervene to accelerate negotiations to acquire full commercial rights to provide certainty and begin marketing them in the UK.

The funding of the championships is underpinned by the public purse. The government has already promised more than £7m in lottery funding through UK Sport and has provided a backstop guarantee should sponsorship and ticket sales not cover costs.

Stewart and Hancock said they “fully supported” a move by the GLA and UK Sport to intervene in the row and put “the proper distance and controls between the board and UKA and to remove the conflict that comes from oversight and delivery functions being in the same hands”.

It is understood that this will be achieved by appointing a new co-chair alongside Warner and replacing Hancock and Stewart, who said that it was better if they stepped aside to try to rebuild trust in the board. Bolton, who said she was leaving for personal reasons, will also have to be replaced.

Sources close to UKA said that there had always been a fundamental reluctance by the two independent directors to acknowledge its expertise in putting on major events, as evidenced by successive Anniversary Games, and that it made sense to sell sponsorship to the championships and the British team as a single package.

Sponsorship sales have been delayed by negotiations with Dentsu, the IAAF partner that requires a fee to release the rights. Warner is believed to have approached the IAAF president, Sebastian Coe, for a financial contribution, arguing that the parlous state of the sport caused by a succession of scandals at the world governing body had hurt commercial prospects.

In a statement, the IAAF said: “These are clearly unsettling events and Sally has been doing a terrific job. As you would expect the IAAF is talking to London 2017 and will continue the dialogue with them.”

Bolton, who joined the organisation in May 2014 after overseeing a successful Rugby League World Cup in 2013 and is understood to have been aligned with Hancock and Stewart, said she was “incredibly proud” of having laid the groundwork for the event.

“I wish the team well in what is going to be an exciting 18 months, and I look forward to seeing some amazing sport take place at next year’s championships,” she said.